Chapter 12: Questions with Calculations

1. What is the period of a sound with a frequency of 10 kHz?

2. What is the wavelength of a sound with a frequency of 20 kHz?

3. Bats emit and listen for ultrasound with a frequency of 50 kHz (and greater!). What is the wavelength of such a wave with a frequency of 50 kHz. Use 345 m/s as the speed of sound in air.

4. Dolphins use ultrasound of 60 kHz or so underwater. The speed of sound in water is about 1500 m/s. What is the wavelength, in the water, of this 60 kHz ultrasound?

5. Normal human hearing has a range of about 60 Hz to 10 kHz in frequency. What is this range in terms of wavelengths? Use the speed of sound in air as 340 m/s.

6. Standing at the edge of a lake you shout and listen as the echo returns from a large cliff at the other side of the lake 4.2 seconds later. How wide is the lake? Use the speed of sound in air as 340 m/s.

7. A guitar string is 0.70 m long and is tuned to play E on the staff (330 Hz) when it is plucked and the whole length is free to vibrate. Where should you place your finger on the string if you want to play A on the staff (440 Hz)?

8. As a train goes by a railroad crossing, you notice that it requires 3 seconds for each car to go by. Each car is 15 meters long. What is the speed of the train?

9. On a winter's day when the air temperature is 0C, what is the speed of sound?

10. On a very hot summer's day when the air temperature is 40C, what is the speed of sound?

11. Dolphins use ultrasound of 50 kHz or so underwater. The speed of sound in water is about 1500 m/s. What is the wavelength, in the water, of this 50 kHz ultrasound?

12. Suppose you listen to sound from a small speaker at a distance of 1.0 m away. Now move to a distance of 4.0 m away. What will have happened to the intensity of the sound?

13. The fundamental frequency of a guitar string, tuned to A, is 440 Hz. What is the frequency of the second and third harmonics of this string?

14. If you strike two tuning forks which oscillate at 256 Hz and 258 Hz, what will you hear as the beat frequency?

15. If you connect two signal generators to an audio speaker and supply sound signals at 505 Hz and 509 Hz, what will you hear as the beat frequency?